This invention relates to the field of mechanical metal deformation processes, and more particularly to brake forming.
The process of brake forming involves placement of a piece of sheet metal along a die and pressing a punch downward onto the die to form the sheet metal along a straight axis in a desired shape. Many shapes can result, but common shapes include a v-shape, channel-shape, and u-shape.
Press brake punches and dies are well known in the art, as are methods of making them. Because punches and dies repeatedly undergo significant forces during brake forming, they are generally made of hardened steel. Such steel must have sufficient hardness to provide the necessary strength and rigidity to maintain the effectiveness and shape of the punch and die over multiple uses.
A major problem with press brake tools is that they wear out quickly. After a certain number of uses, abrasion and galling cause deformation of the punch and the die. Because precision in brake forming is often critical, when the punch or the die begins to lose its shape, the press operator must make adjustments to the forming process, replace the punch or die, or repair the punch or die. Replacement and repair of punches and dies contribute to the costs of the brake forming process, as does having to shut the press down during the re-tooling.
It is therefore desired to develop a punch and a die that better resist wear from repeated use, but that do not significantly increase the costs of manufacture or decrease the performance of the press brake. In the past, dies have been created with inserts to decrease friction. For example, the invention of U.S. Pat. No. 3,914,972 includes a die having rotatable inserts made from an anti-friction material, such as TEFLON. However, being made from anti-friction material, these inserts cost more to produce, and must be replaced more often, than inserts made of harder, less expensive materials, such as steel. Further, because of the reduced hardness of such inserts, dies having these inserts may not be useable with some types of hardened sheet metal.
In addition, press brakes have been created in the past that include a removable punch insert and a removable die portion. For example, the invention of U.S. Pat. No. 5,878,619 includes such a system. However, these types of tool systems do not sufficiently reduce the expense of press braking. First, the removable punch insert does not comprise the entire bending surface of the punch, and therefore the punch itself undergoes wear from the press braking process and must be periodically repaired or replaced. In addition, the removable punch insert can be expensive to make because it is an intricate part that contains several different bending surfaces of different radii, each of which must be separately tooled to precise measurements. Second, the removable die portion does not sufficiently reduce expenses because it itself is the tool used to shape the metal, and is therefore susceptible to substantial wear. The removable die portion is expensive to repair or replace because it consists of the entire portion of the bending surface of the die and thus must be machined to the desired shape and radius.